【作者】 鲁照玲；

【导师】 郭兴蓬；

【作者基本信息】 华中科技大学 ， 材料物理与化学， 2007， 博士

【摘要】 溶液pH值的变化引起金属表面状态的变化,不仅对金属腐蚀行为有较大的影响,也会对缓蚀剂的吸附和缓蚀行为及相应的缓蚀机理等产生重要影响。关于CO2腐蚀用缓蚀剂的性能评价和机理研究,大部分工作是在含有CO2的酸性环境下进行,对于近中性环境下(例如油田产出水等)缓蚀剂的吸附和缓蚀行为尚缺乏系统性的研究。由于缓蚀剂的性能对环境有明显的依存性,在酸性环境下性能好的缓蚀剂在中性环境下常常表现不好,反之依然。对在近中性环境下缓蚀剂的吸附和缓蚀行为及相应缓蚀规律和机理的研究,不仅有助于阐释缓蚀剂随应用环境的变化相应缓蚀机理的差异,也能为近中性环境下缓蚀剂的选择和设计提供重要的参考依据。本研究采用具有简单分子结构的十二胺(有机碱)和月桂酸(有机酸)作为模型缓蚀剂,主要采用电化学和表面分析等方法,系统地研究了N80碳钢在近中性CO2饱和盐水溶液中的腐蚀行为及腐蚀机理;有机碱和有机酸在近中性CO2饱和盐水溶液中的吸附和缓蚀行为以及相应的缓蚀机理;同时也对近中性环境下有机碱和有机酸与腐蚀产物的相互作用进行了探讨。研究结果表明在近中性的CO2饱和盐水溶液中金属的腐蚀行为依赖于溶液的pH值。pH< 6.8,腐蚀的阴极过程受电化学反应过程控制;pH >6.8,腐蚀的阴极过程受传质过程控制;随溶液pH值的进一步增加,腐蚀的阴极过程受电化学反应和传质过程的混合控制。对腐蚀的阳极过程而言,pH<5.9,金属呈活性溶解的状态;pH 6.5时金属呈过渡态特征;pH >6.8,可以观察到典型的阳极钝化行为,在金属表面能够形成连续的腐蚀产物保护膜,但过高pH值会加快腐蚀产物膜的溶解。十二胺对金属的保护作用强烈地依赖于溶液的pH值,随溶液pH值的增加,十二胺的缓蚀性能增加,最低有效缓蚀浓度降低。在低pH值下,十二胺主要抑制金属腐蚀的阴极过程;在近中性pH值下,十二胺同时抑制金属腐蚀的阴、阳极过程。对缓蚀剂吸附状态的研究表明十二胺主要以未质子化的分子状态吸附在金属表面。在低pH值时,缓蚀剂分子主要以十二胺鎓离子的形式存在,荷正电的金属表面不利于鎓离子的吸附,金属表面分子吸附状态可能起因于十二胺鎓离子在金属阴极部位的还原吸附。高pH值时,缓蚀剂分子以分子状态存在的比例增大,分子状态的十二胺分子氮原子上的电子云密度比质子化状态时更大,使得在高pH值下缓蚀剂分子与金属原子的空‘d’轨道具有更强的配位能力,因此具有较大的吸附能力和吸附稳定性。从酸性到近中性pH值范围内,月桂酸抑制金属腐蚀的能力同样依赖于溶液的pH值。随溶液pH值的增加,月桂酸对金属腐蚀的抑制能力降低,相应的最低有效缓蚀浓度增加。月桂酸在金属表面上的吸附状态与在溶液中的存在状态不尽相同,低pH值时,月桂酸根离子在静电作用下吸附在金属表面,显著地改变了金属表面的荷电状态,使金属表面呈现电中性,有利于分子状态的月桂酸的进一步吸附,吸附的月桂酸分子中的羧基与呈活性溶解状态的金属发生化学键合,因此可以有效阻止金属腐蚀过程的进行。高pH值时,虽然呈阴离子状态的月桂酸根离子容易吸附在荷正电荷的金属表面,但是缓蚀剂的吸附并不能显著改变金属表面的电荷状态。另外在高pH值的条件下金属覆盖有一层保护性的腐蚀产物层,月桂酸根离子可能不容易在腐蚀产物表面附着吸附,因此在高pH值下缓蚀剂并不能完全阻止金属的腐蚀作用。腐蚀产物膜与缓蚀剂之间的相互作用与缓蚀剂的类型和溶液pH值相关。pH 6.9时十二胺对FeCO3晶体形貌影响不大,但月桂酸对FeCO3晶体存在明显的溶蚀作用;两种缓蚀剂对于FeCO3晶粒的进一步形成均有一定程度的抑制作用,缓蚀剂的加入降低了金属表面上的覆盖层与金属基体之间的结合力;十二胺对金属表面腐蚀产物膜的保护作用起正面的效果,而月桂酸的效果则相反。pH 7.4时,十二胺和月桂酸的加入虽然对FeCO3晶粒的形成仍然有一定程度的抑制作用,但缓蚀剂的加入却极大地促进了FeCO3晶粒的细化和有序排列,有效地提高了覆盖层与金属之间的结合力;十二胺和月桂酸不仅能有效抑制均匀腐蚀,同时还能降低N80碳钢对局部腐蚀的敏感性,其中十二胺的作用效果更加明显。更多还原

【Abstract】 The change of the metal surface state with the change of pH value not only has influence on the corrosion behavior of the metal, but also can effect significantly on the adsorption behavior, inhibition efficiency and the inhibition mechanism of the inhibitors. Much work about the performance evaluation and mechanism investigation of the inhibitors is carried out in the CO2-containing acidic environment, less work in the near neutral environment such as the produced water containing CO2 in oil gas industries. The performance of the inhibitors is much environment-dependent, the inhibitors which behave well in acidic environment might have no role in neutral environment and vice verse. The investigation about the adsorption behavior, inhibition performance of the inhibitors in near neutral environments will facilitate not only to the better understanding of the inhibition mechanism of the inhibitors but also to the effective selection and successful design of new inhibitors in the near neutral environments.Dodecylamine (organic alkali) and lauric acid (organic acid) which have the simple molecule structures were considered as the model inhibitors in this work. Electrochemcal methods and surface analysis methods were used to investigate the corrosion behavior and the corrosion mechanism of N80 carbon steel in near neutral CO2-saturated brine solution. The inhibition performance, adsorption behavior and the inhibition mechanism of the inhibitors in near neutral environments were also investigated. Furthermore, the interaction between the inhibitors and the corrosion products formed in near neutral environments were studied.The results have shown the corrosion behavior of carbon steel was dependent on pH value of the solution. The cathode reaction of the corrosion was controlled by the electrochemical reaction in the range of pH< 6.8, and the determining process was transfered to a mass-diffusion process when pH> 6.8. With the further increase of pH value, the cathode reaction was controlled by both the electrochemical and mass-diffusion processes. For the anode reaction, the metal was in the active dissolution state in the range of pH< 5.9. The metal state has the characteristics of the transition state at pH 6.5;When pH> 6.8, the typical passivation phenomena was observed, and the complete and continuous corrosion product film formed on the metal surface. However, the higher pH value enhanced the dissolution action of the corrosion products.The inhibition ability of dodecylamine was strongly dependent on pH value of the solution and improved with the increase of pH value. The minumum effective inhibitor concentration reduced distinctly with the increase of pH value. At lower pH value, dodecylamine inhibited mainly the cathode process; while it inhibited both the anode and cathode processes in near neutral environments. At lower pH value, the adsorption state of the inhibitor was mainly the unprotonated dodecylamine. It was unfavorable to adsord on the metal surface with the positive net charge. The adsorption state of dodecylamine on the metal surface might be attributable to the adsorption of the unprotonated dodecylamine after the reduction of the dodecylamine onium on the cathode site. The ratio of the unprotonated to the protonated of dodecylamine increased with the increase of pH value, which was favorable to the adsorption of the inhibitor. The higher electron cloud density of the unprotonated provided much stronger coordination with the ’d ’ orbital of the metal atom and hence the adsorbed inhibitor was more stable and tight on the metal surface.Lauric acid reduced the corrosion rate of N80 carbon steel both in acidic and near neutral environments. The inhibition ability and the minimum effective inhibitor concentration were both pH-dependent. The former decreased and the latter increased with pH value. Lauric acid inhibited mainly the anode reaction in the test pH values. The adsorption state of the inhibitor was not totally consistent with that in the solution. At lower pH value, laurate adsorbed on the metal surface by the electrostatic interaction and changed the charge state of the metal surface from the positive to the electrically neutral. The carboxyl group bonded chemically with the metal in the active-dissolution state. At higher pH values, although the net charge state was favorable to the adsorption of laurate, the adsorption of the inhibitor had no obvious influence on the charge state of the metal surface. Besides, the protective corrosion product film was formed at higher pH value which was favorable to the adsorption of the inhibibitor and hence did not prevent the corrosion effectively.The interaction between the inhibitors and the corrosion products in near neutral environments has relation with the type of the inhibitors and pH value of the solution. At pH 6.9, dodecylamine has no obvious influence on the morphology of FeCO3 crytal, while lauric acid has obvious dissolution-erosion action to FeCO3 crystal. Both inhibitors have some inhibitive role to the formation of FeCO3 crystal and the addition of the inhibitors reduced the adhesion strength of the film on the metal surface. Dodecylamine has certain positive role to the protection ability of the film while lauric acid on the contrary. At pH 7.4, both of dodecylamine and lauric acid contributed to the grain refinement and orderly arangement of FeCO3 crystals. The adhesion strengths of the corrosion product film were enhanced in both cases. Dodecylamine and lauric acid not only inhibited the uniform corrosion, but also reduced the sensitivity of the metal to the localized corrosion and the former was more obvious than the latter.更多还原